Cardiac Fibers and Action Potential

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What happens to the conduction velocity in certain cells?

It fluctuates randomly

It becomes progressively faster

It remains constant

It becomes progressively slower (correct)

What happens to the membrane potential in hyperkalemia?

It fluctuates randomly

It becomes less negative (correct)

It becomes more negative

It remains constant

What is the correct order of the conduction system in the heart?

AV node – SA node – Bundle of His – Purkinje fibers

Bundle of His – AV node – Purkinje fibers – SA node

Purkinje fibers – Bundle of His – AV node – SA node

SA node – AV node – Bundle of His – Purkinje fibers (correct)

What can cause fast responses of cardiac muscle to change to slow responses?

Hypoxia due to ischemia Signup and view all the answers

What is the result of a lack of blood supply to a region of cardiac muscle?

Ischemia Signup and view all the answers

What is the starting point of the conduction of the heart?

SA node Signup and view all the answers

What can happen to the fast sodium channels in high potassium levels?

They are inactivated Signup and view all the answers

What can be a consequence of hyperkalemia?

Arrhythmias and death Signup and view all the answers

What can cause a region of cardiac muscle to become ischemic?

Coronary artery disease Signup and view all the answers

What is the velocity of action potentials spreading throughout the atria?

0.5 m/s Signup and view all the answers

What is the function of the AV node in the cardiac conduction system?

To slow down the impulse conduction Signup and view all the answers

What is the region where the AV node is located?

Inferior-posterior region of interatrial septum Signup and view all the answers

What is the characteristic of the AV node?

Highly specialized conducting tissue Signup and view all the answers

What happens to the impulse conduction velocity in the AV node?

Decreases from 0.5 m/s to 0.05 m/s Signup and view all the answers

What is the characteristic of the N region of the AV node?

Displays post repolarization refractoriness Signup and view all the answers

What is the function of Bachmann's bundle?

Conducts impulses from the SA node directly to the left atrium Signup and view all the answers

How do impulses from the SA node spread in the right atrium?

Radially throughout the right atrium along the ordinary myocardial fibers Signup and view all the answers

What is the sequence of cardiac electrical activation?

SA node → Atria → AV node → Ventricles Signup and view all the answers

What is the responsible ion for the start of rapid upstroke of the QRS depolarization in Phase 0?

Na Signup and view all the answers

What type of cardiac fibers are responsible for producing fast-response action potentials?

Atrium, ventricles, and Purkinje fibers Signup and view all the answers

What is the duration of the action potential in fast-response cardiac fibers?

Longer due to the plateau phase Signup and view all the answers

What happens to the inside of the cell during Phase 0?

It becomes more positive Signup and view all the answers

What is the role of the plateau phase in fast-response cardiac fibers?

Allows for ventricular filling Signup and view all the answers

Which phase corresponds to the ST segment of the ECG?

Phase 2 Signup and view all the answers

What is responsible for the relatively prolonged duration of the cardiac myocyte electrical cycle?

Balance between Ca++ and K+ Signup and view all the answers

What is a characteristic of slow-response cardiac fibers?

The resting potential is less negative Signup and view all the answers

Which phase is absent in slow-response cardiac fibers?

Phase 1 Signup and view all the answers

What happens to most fast Na+ channel gates during Phase 2?

They close Signup and view all the answers

What is true about the ERP (Effective Refractory Rate)?

Fast sodium channels are inactivated Signup and view all the answers

What is the result of the balance between the inward flow of Ca++ and outward flow of K+ in Phase 2?

No net current flow between cells Signup and view all the answers

What happens to some K+ ions during Phase 2?

They exit the cell through slow K+ channels Signup and view all the answers

What is the function of the ERP (Effective Refractory Rate)?

Prevents the heart from having compounded action potentials Signup and view all the answers

What is the purpose of the plateau phase in fast-response cardiac fibers?

Allows for ventricular filling and prevents compounded action potentials Signup and view all the answers

What happens to some Ca++ ions during Phase 2?

They enter the cell slowly through slow channel gates Signup and view all the answers

What is the difference between fast-response and slow-response cardiac fibers?

Fast-response has a longer duration of action potential Signup and view all the answers

What happens to repolarization by the end of Phase 2?

It continues Signup and view all the answers

What is responsible for the plateau of the ventricular action potential?

A slow inward Ca2+ current Signup and view all the answers

What is the result of an outward K+ current in cardiac tissues?

Repolarization of the cell membrane Signup and view all the answers

What is responsible for the pacemaker property of sinoatrial (SA) nodal cells?

An increase in Na+ conductance Signup and view all the answers

What is Phase 4 in cardiac tissues?

Electrical diastole Signup and view all the answers

What is the function of gap junctions in cardiac tissues?

To provide low-resistance sites of current spread Signup and view all the answers

What type of current is responsible for the upstroke of the action potential in the sinoatrial (SA) node?

A rapid inward Ca2+ current Signup and view all the answers

What is the result of an increase in Na+ conductance in sinoatrial (SA) nodal cells?

Depolarization of the cell membrane Signup and view all the answers

What type of current is responsible for the pacemaker property of sinoatrial (SA) nodal cells?

An inward Na+ current Signup and view all the answers

What is the role of the sinoatrial (SA) node in the heart?

To generate the heartbeat Signup and view all the answers